Building on our previous work with antiviral drugs active against EBV we propose six specific aims to address fundamental issues posed by EBV infection: productive and persistent infection, latency, drug resistance, reversibility of drug effect, and cellular transformation. The first and third aims are designed to coupled investigation of new drugs or drug combinations with EBV biologic systems. Synergistic combinations (aim 2) of drugs with different modes of action may offer an approach to combat drug- resistance, reversibility and reduce cytotoxicity. The second aim deals with the mode of action of the drugs in general and AZT in particular. Based on what we have learned from our studies with ACV, DHPG, BVdU, FMAU and FIAC we will investigate (a) drug phosphorylation, (b) role of EBV TK, (c) interaction of EBV polymerase with drug-triphosphates, (d) chain termination, (e) drug incorporation, (f) reversibility, (g) role of thymidylate kinase, and (h) drug-binding domains. In the fourth aim we will use mutated EBV polymerase-expressing cell lines generated by site- directed mutagenesis to study cross-resistance to the new drugs. In the fifth aim we present a plan to disrupt or cure EBV episomal maintenance with synthetic EBNA-1 antisense methylated oligonucleotides by blocking synthesis of EBNA-1 protein needed for binding to the EBV ori-P. The final aim deals with blocking EBV-induced transformation by selected new drugs and interferon alpha and gamma, coupled with use of EBNA-1 antisense oligonucleotides to reduce episomal numbers during transformation. Data obtained from these studies will facilitate understanding of mechanisms of drug action, help in the development of selective antiviral agents, and open new approaches to dealing with EBV infection.